Over the past century, a variety of different types of lightbulbs have been developed. The most common type of lightbulb is the incandescent bulb, in which electric current is passed through a metal filament disposed in a vacuum, causing the filament to glow and emit light. Another common type of lightbulb is the fluorescent light.
Recently, bulbs have been developed that produce illumination in a different manner, in particular through the use of light emitting diodes (LEDs). Pre-existing LED lightbulbs have been generally adequate for their intended purposes, but they have not been satisfactory in all respects.
As a first aspect of this, above a temperature of about 25° C., an LED operates less efficiently and produces less light than at lower temperatures. In particular, as the operating temperature progressively increases above 25° C., the light output of the LED progressively decreases. One approach to heat dissipation is to simply provide a heat sink. But although a heat sink can spread the heat, it does not remove the heat effectively from the vicinity of the LEDs, which reduces the brightness of the LEDs and shortens their operational lifetime. Consequently, efficient dissipation of the heat produced by the LEDs is desirable in an LED lightbulb.
A further consideration is that an LED lightbulb typically needs to contain some circuitry that will take standard household electrical power and convert it to a voltage and/or waveform that is suitable to drive one or more LEDs. Consequently, a relevant design consideration is how to package this circuitry within an LED lightbulb.
In this regard, it can be advantageous if the LED lightbulb has the size and shape of a standard lightbulb, including a standard base such as the type of base commonly known as a medium Edison base. However, due to spatial and thermal considerations, existing LED lightbulbs have not attempted to put the circuitry in the Edison base. Instead, the circuitry is placed at a different location, where it alters the size and/or shape of the bulb so that the size and/or shape differs from that of a standard lightbulb. For example, the bulb may have a special cylindrical section that is offset from the base and that contains the circuitry.